What are third party cookies?
Third party cookies are set by a domain other than the site you are visiting, historically the glue of cross site tracking: following users between sites to target, retarget and attribute. First party cookies belong to the site itself and mostly survive; the third party kind is being phased out of the ecosystem.
What is disappearing with them
- Cross site retargeting pools: smaller and blinder than they were.
- View through measurement: journeys across sites and devices increasingly invisible to click based tools.
- Cheap audience data: the third party segments marketers rented for years, built on exactly this plumbing.
Why it matters
The marketing stack of the 2010s assumed individual level tracking everywhere. That assumption is gone: browsers block, regulators restrict, users decline. Brands that waited for a reprieve lost years; the direction of travel has never changed.
What replaces them
A portfolio, not a plug in: first party data collected with real consent, server side tracking and Conversion APIs to keep signals flowing, contextual targeting that needs no identity, and Media Mix Modelling for measurement that never needed cookies in the first place. The winners treat privacy as the operating condition, not the obstacle.
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